The present invention relates to a push lock mechanism employable for a push switch or the like, and more particularly to a push lock mechanism using a cam lock mechanism consisting of a heart-shaped cam groove and a driving pin for locking an operation shaft when the shaft is pushed once and releasing the locked position when the shaft is pushed again.
In this type of push lock mechanism as known, a slider having the heart-shaped cam groove on its peripheral surface is fixed to the operation shaft, and the driving pin is rockably supported to a case in opposed relationship to the slider. The driving pin is designed to trace in the heart-shaped cam groove in association with the reciprocating motion of the slider. In operation, when the operation shaft is pushed (moved forwardly) against a return spring, the driving pin is shifted to a locked position in the heart-shaped cam groove to thereby lock the operation shaft with the slider in the depressed position. When the operation shaft is pushed again under the locked condition, the driving pin is shifted to an unlocked position in the heart-shaped cam groove to thereby release the locked condition of the operation shaft. Then, the operation shaft is returned (moved reversely) to its original position. In the case that a sliding contact is provided on the slider, and a contact adapted to contact the sliding contact is provided on the case, for example, a switching operation between the contact and the sliding contact may be effected by operating the operation shaft. Furthermore, a switched condition may be maintained by the locking operation as mentioned above.
However, in the conventional push lock mechanism, when the operation shaft is pulled under the locked condition, the slider is also pulled together with the operation shaft. Accordingly, undue force is applied to the engaged portion between the heart-shaped cam groove and the driving pin, causing breakage of a cam surface of the heart-shaped cam groove and deformation of the driving pin. As a result, the subsequent locking operation is rendered unreliable. To cope with this problem, a handle to be mounted on the operation shaft has been designed in such a shape that the handle cannot be easily pulled by an operator. However, there remains a possibility that the handle could be pulled. Thus, it is considered that such measures cannot reliably protect the push lock mechanism. In addition, there is another problem that the design of the handle is limited.